1. Field of the Invention
The present invention relates to hydrostatic radial piston machines and, more particularly, is concerned with the driving means to power such machines.
2. Description of the Prior Art
Hydrostatic machines convert rotary mechanical motion, typically from an internal combustion engine, to fluid motion in the case of a hydraulic pump, whereas when the pump is combined to a hydraulic motor as in a hydrostatic transmission, fluid motion is converted back to mechanical motion to rotate for example, a drive axle of a vehicle such as a lawn and garden tractor.
The hydrostatic machine operating as a pump regulates or controls the flow output such that varying rates of fluid flow are attainable with a single speed input rotary mechanical motion. Within the hydrostatic machine of the radial piston type, a cylinder barrel rotates on a fixed pintle valve with pistons positioned within the cylinders and attached to slippers such that as the cylinder barrel rotates, the pistons engages a surrounding annular track ring. When the track ring is set in eccentric relationship with the pintle valve, the pistons displace fluid from their respective cylinders and the fluid is expelled from the hydrostatic machine. The rate of fluid delivered is therefore directly proportional to the eccentricity of the track ring of the machine relative to the pintle valve.
The eccentricity of the pump track ring must therefore be variable and this, for example, can be accomplished by pivotting the track ring around an axis located at one end of the track ring, the axis definer generally being a pivot pin. In addition, a control mechanism adapted to swing or pivot the track ring around the pivot axis must also be provided allowing the eccentricity of the track ring to be changed. Such a hydrostatic machine is shown in U.S. Pat. No. 5,078,659, entitled VARIABLE SPEED TRANSAXLE, issued Jan. 7, 1992, which is specifically incorporated herein by reference.
The hydrostatic transmission is totally encapsulated inside a purposely formed internal chamber inside the transaxle housing structure, and comprises a hydraulic pump is fluidly coupled to the hydraulic motor. The motor is connected through reduction gearing and differential to the output axle shafts on which the wheels of the vehicle are attached.
A bevel pinion gear attached and driven by the vertically aligned input shaft of the transaxle is used in combination with a larger bevel gear and engaged by drive dogs to the cylinder barrel of the hydraulic pump. The bevel gear is supported by means of a bearing on the cylindrical pintle valve.
During the development of the hydrostatic transaxle, it was found that a serious problem existed due to the excessive tilting or deflection of the bevel gear during power transmission. This not only resulted in poor operating efficiency, but on occasion was so severe that the cylinder barrel seized onto the pintle valve.